1. Field of the Invention
The present invention relates to a projection system employing a plurality of lamps and a plurality of light valves, in particular, three lamps and three light valves.
2. Description of the Related Art
Light valves operating in a transmission or reflection mode, using liquid crystal, moving mirror, oil film, or other technologies are known for modulating a cross section of a light beam in two dimensions in response to a control signal. A key use of such light valves is in systems employing rear or front projection of light to display video images, in particular color video images.
A prior art light valve projection system sold by General Electric Company under the name "Talaria" utilized three lamps and three light valves. Each lamp was focused through associated dichroics onto a different associated one of the light valves. Each lamp and its associated dichroics and light valve produced an output beam at a different one of the three primary colors, red, green and blue. The disadvantage of this system is that because only one primary color is obtained from each lamp, only about 1/3 of the total output of the lamps is utilized.
It is also known from commonly owned U.S. Pat. No. 4,684,390 to separate light from a single lamp into three primary colors and apply each color to a different one of three light valves. One suitable lamp for this configuration is a 100 W UHP lamp from Philips Lighting. Because, brightness of the image produced may be marginal for large displays, this patent suggests the possibility of using two such lamps in closely spaced relationship. Also, the use of equal path lengths from the illumination subsystem to each of the light valves is disclosed.
Commonly-owned U.S. Pat. No. 5,386,250 describes a two lamp, one light valve projection system in which the two lamps are alternately active and a single light beam produced from the two sources by combining with a DMD is passed through a color wheel synchronized with the alternation of the lamps to illuminate the light valve sequentially with light of the three primary colors. In such a color sequential illumination system, color artifacts may be produced in the projected image because only one primary color is projected at a time. It should be understood that in such a prior art single light valve system, in order modulate each of the three primary colors during each field, the light valve must operate color sequentially at three times the field rate.